On Sat, 03 Sep 2011 15:51:10 -0700, Jeff Liebermann
wrote:

Few Caps exhibit 0.01uF (when so marked) to transients (where it is
presumed they will exhibit 1/2*pi*f*c reactance to the risetime).

True. They all have some internal resistance to overcome.

It goes beyond that. Extrapolating from power applications hides the
defects of ceramic.

At HF/VHF and above, successful applications comes from throwing uF
solutions at pF problems. Ceramic's performance reveals inductive
reactance above 1-10 MHz. ESR also exhibits the same turn-around in
the same frequency range. Ceramic temperature coefficient is (Y5V)
goes into the toilet in weather that most of the south and eastern
seaboard has seen this summer. XR7 voltage coefficient causes
capacity to plummet at the voltages you offer for static. Over time,
ceramics lose capacity for simply having been in service for a while.

Aside from that, they work fine.

I was a big fan of porcelain caps from AVX in big
power amps. If you wanna handle current, there's nothing better.

However, those ceramics are 1,000 times (min.) larger than what you
have recommended. They serve an entirely different agenda.

AVX discusses these issues in much the same terms (for those larger
caps too) at:
http://www.avx.com/docs/techinfo/mlc-tant.pdf

Incidentally, I don't think they make 0.01uF silver mica caps. The
biggest I played with were in antenna tuners at 4700pF

Where there is every chance that one silver mica head-to-head with the
ceramic actually exhibit better performance (protecting the diodes).
Perhaps with the scarcity of silver mica, however, 10uF ceramics would
make do (it is not like any precision is demanded to force a selection
of 0.01uF which is boilerplate recommendation from the 50s).

73's
Richard Clark, KB7QHC

On Sat, 03 Sep 2011 22:29:49 -0700, Richard Clark
wrote:

At HF/VHF and above, successful applications comes from throwing uF
solutions at pF problems.

That's not a problem. In order to get obtain decent bypassing across
5 octaves of bandwidth (2-30MHz), one needs to have multiple capacitor
values and types in parallel. The self-resonant characteristics of
the capacitors is the limiting factor. At some frequency, every
capacitor, and its associated lead inductance, will exhibit an
impedance dip commonly known as series resonance. Below this
frequency, the capacitor will look ummm... like a capacitor. Above
this frequency, it will be more like an inductor.
http://www.ecircuitcenter.com/Circuits/cmodel1/cmodel1.htm

None this has anything useful to do with the 0.01uf caps in the
instrument. The diodes are in series with 47K resistors, which are
much larger than any inductive reactance that the 0.1uf bypass
capacitor might present. Since the MFJ-259b only works well up to
maybe a 10:1 VSWR or 5Kohms, the 47K is sufficiently larger than
whatever reactance is presented by the 0.01uf to make the capacitor
characteristics to not be an issue.

While component selection and circuit design are interesting topics,
the current problem is MFJ design quality, MFJ-259b, ESD protection,
and chronic detector diode failures.





--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558